Effects of plants competition on critical bacteria selection and pollutants dynamics in a long-term polyculture constructed wetland.

The effects of mix planting on the functions of plants, microorganisms, and their interactions were studied in a CW planted with Phragmites australis and Typha orientalis over six years. Findings show notable competition among plant species, with excessive overgrowth of the dominant species (P. australis) over T. orientalis. The excessive outcompeting by P. australis resulted in significantly higher plant density and biomass of 20.1 times and 11.2 times, respectively than that of T. orientalis. Interspecific competition appeared to considerably intensify plants contributions to nitrogen and phosphorus removal, which increased from circa 9% in the first year up to 42% in the sixth year. High-throughput pyrosequencing and network analyses demonstrated that the dominant species stands harbor diverse bacterial communities that could enhance the wetland performance through carbon degradation, nutrient cycling, and supporting plant growth. These results provide useful insights into the interactive effects of plants and bacteria in polyculture constructed wetlands.